Epilepsy and intellectual disability: Does epilepsy increase the likelihoodof co-morbid psychopathology?

Saadia Arshad, Robert Winterhalder, Lisa Underwood, Katerina Kelesidi, Eddie Chaplin,Eugenia Kravariti, Dimitrios Anagnostopoulos, Nick Bouras, Jane McCarthy, Elias Tsakanikos *

Estia Centre, Institute of Psychiatry, King’s College London, 66 Snowsfields, London SE1 3SS, UK

Epilepsy is a particularly common condition among people with intellectual disability (ID) (Bhaumik, Tyrer, McGrother, &Ganghadaran, 2008; Fitzgerald & Ring, 2009). A large community-based survey has revealed a prevalence rate of 22.1%,making epilepsy the second most common co-morbid condition in adults with ID (Welsh Office, 1995). The estimatedprevalence of epilepsy in adults with ID living in community is about 16% compared with 0.4–1% in the general population(Morgan, Ahmed, & Kerr, 2000). Although the psychosocial impact of epilepsy in adults with ID is pervasive (Kerr, Turky, &Huber, 2009) it remains unclear whether epilepsy per se can increase the likelihood of psychopathology.

It has been suggested that epilepsy can be a risk factor for the development of mental health problems in people with ID(Lund, 1985; Deb & Hunter, 1991) and it has been associated with poor social and adaptive skills (Matson, Bamburg, & Mayville,1999). Possible explanations include the impact on well-being and quality of life, as well as the possibility that atypicalneurodevelopment in ID may also predispose to both epilepsy and mental illness. Nevertheless, more recent evidence(Matthews, Weston, Baxter, Felce, & Kerr., 2008; Pawar & Akuffo, 2008; Turkistani, 2004) has shown that the presence ofepilepsy does not increase the incidence of mental illness among people with ID. This was supported by trends being observedtowards lower rates of mental health problems among those with epilepsy (Matthews et al., 2008; Pawar & Akuffo, 2008;Turkistani, 2004) although these results failed to reach statistical significance, perhaps due to sample size limitations. It isconceivable that lower rates of mental health problems among patients with epilepsy could be accounted for by the calming,mood-stabilizing effects of anti-epileptic drugs (Johannessen, 2008; Rogawski & Loscher, 2004) as well as possible diagnosticovershadowing (Mason & Scior, 2004).

Research in Developmental Disabilities 32 (2011) 353–357

A R T I C L E I N F O

Article history:

Received 6 October 2010

Accepted 15 October 2010

Keywords:

Co-morbid psychopathology

Epilepsy

Intellectual disabilities/mental retardation

Mental health needs

Specialist services

A B S T R A C T

Although epilepsy is particularly common among people with intellectual disability (ID) it

remains unclear whether it is associated with an increased likelihood of co-morbid

psychopathology. We therefore investigated rates of mental health problems and other

clinical characteristics in patients with ID and epilepsy (N = 156) as compared to patients

with ID but no epilepsy (N = 596). All participants were consecutive referrals to specialist

mental heath services. Specialist clinicians agreed on the mental health diagnoses by

applying ICD-10 clinical criteria using information gained from interviews with key

informants and the patients. Bivariate and multivariate analyses showed that patients

with epilepsy were more likely to live in residential housing and have severe ID in line with

previous evidence. However, the presence of epilepsy was not associated with an

increased likelihood of co-morbid psychopathology. On the contrary, rates of mental

health problems, including schizophrenia spectrum, personality and anxiety disorders,

were significantly lower among patients with epilepsy. The results are discussed in the

context of mood-stabilizing and other psychotropic effects of anti-epileptic drugs in adults

with ID and epilepsy, as well as possible diagnostic overshadowing.

� 2010 Elsevier Ltd. All rights reserved.

* Corresponding author. Tel.: +44 20 3228 9745.

E-mail address: elias.tsakanikos@kcl.ac.uk (E. Tsakanikos).

Contents lists available at ScienceDirect

Research in Developmental Disabilities

0891-4222/$ – see front matter � 2010 Elsevier Ltd. All rights reserved.

doi:10.1016/j.ridd.2010.10.013

There is currently limited research in understanding the relationship between epilepsy and psychopathology in adultswith ID (Fitzgerald & Ring, 2009; Matthews et al., 2008). In addition, the role of potentially mediating variables oftenassociated with epilepsy, such as severity of ID and age are little understood (Branford, Bhumick, & Duncan, 1998;McDermott et al., 2005). We therefore examined whether epilepsy was associated with rates of co-morbid psychopathologyand other clinical characteristics after statistically controlling for potentially mediating variables in a large sample ofpatients with ID referred to specialist mental health services.

1. Methods

1.1. Participants

We included patients with ID and epilepsy (N = 156; 128 generalised and 28 localised) and patients with ID but withoutepilepsy (N = 596). The majority of the patients (about 60%) were males. All participants were consecutive referrals forassessment to specialist mental heath services of South-East London over a period of 20 years. Two specialist psychiatrists inID agreed on psychiatric diagnoses by applying ICD-10 clinical criteria using information gained from interviews with keyinformants and the patients themselves. The interviews were undertaken as part of the clinical assessment and includedhistorical details from past medical and other records.

1.2. Data recording

Co-morbid mental illness was coded according to the following major ICD-10 categories: ‘schizophrenia spectrum disorder’(F20–27), ‘personality disorder’ (F60–69), ‘anxiety’ (F40–48), ‘depressive disorder’ (F32–39), ‘adjustment reaction’ (F43), and‘dementia’ (F00–03). Other recorded variables were: ‘age’, ‘gender’, ‘level of ID’, ‘current housing status’, ‘sources of referral’,‘care pathways’, ‘type of medication’, and ‘active epilepsy’. ‘Active epilepsy’ was operationally defined as having at least oneseizure in the last 2 years. The degree of ID was coded on ICD-criteria into mild (F70), moderate (F71) or severe (F72–73).

1.3. Data analysis

The Statistical Package for Social Sciences, 18th Version (SPSS 18) was employed. Before the analysis, dummy variableswere created for each variable, coded as presence (1) or absence (0). The obtained categorical data were initially analyzed bychi-square tests to examine statistically significant differences between patients with and without epilepsy. The data werefurther analyzed by logistic regression using a stepwise forward method. The variables were added successively according tothe magnitude of their correlation with the dependent variable, and then were successively removed until the predictiveability of the regression model, indexed by the model chi-square, was not significantly improved.

2. Results

Table 1 presents the demographic characteristics of participants with and without epilepsy. There were no statisticallydifferences for age, gender or ethnicity between those with and without epilepsy. However, level of ID yielded statistical

Table 1

Demographic information by the presence of epilepsy.

Epilepsy, n (%) No epilepsy, n (%)

Gender

Male 87 (55.8%) 369 (61.9%)

Female 69 (44.2%) 227 (38.1%)

Age (years)

<24 55 (35.3%) 194 (32.6%)

25–34 45 (28.8%) 155 (26.0%)

35–44 28 (17.9%) 126 (21.1%)

45–54 18 (11.5%) 70 (11.7%)

55+ 10 (6.4%) 51 (8.6%)

Ethnicity

White 454(76.2%) 132 (84.6%)

Black 99 (16.6%) 14 (9%)

Asian 24 (4%) 6 (3.8%)

Other 19 (3.2%) 4 (2.6%)

Level of ID

Mild (F70) 68 (43.6%) 408 (68.5%)

Moderate (F71) 36 (23.1%) 133 (22.3%)

Severe (F72–73) 52 (33.3%) 55 (9.2%)

Housing

Family home 76 (48.7) 279 (46.8)

Residential 17 (10.9) 35 (5.9)

Independent 9 (5.8) 78 (13.1)

Supported 54 (34.6) 204 (34.2)

S. Arshad et al. / Research in Developmental Disabilities 32 (2011) 353–357354

differences with severe level of ID being more prevalent in the group with epilepsy (x2ð1Þ ¼ 62:60, p< 0.001). Differences in

the type of housing were also statistically significant (x2ð1Þ ¼ 10:34, p< 0.001) with patients in the epilepsy group more likely

to live in a residential home rather than independently.Table 2 presents the prevalence of co-morbid psychiatric disorders for patients with and without epilepsy. Patients with

epilepsy were more likely to have no psychiatric disorder than those without epilepsy (x2ð1Þ ¼ 33:20, p< 0.001). Further,

rates of schizophrenia spectrum and personality disorder were significantly lower in the epilepsy group (x2ð1Þ ¼ 15:01 and

x2ð1Þ ¼ 3:91, ps< 0.001 respectively). In terms of medication, significant differences were found between the groups for most

medication treatments. More specifically, rates of psychotropics (x2ð1Þ ¼ 35:35, p< 0.001), PRN (x2

ð1Þ ¼ 5:78, p< 0.001) andno medication (x2

ð1Þ ¼ 79:06, p< 0.001) were significantly lower in the epilepsy group, although combinations weresignificantly higher in the epilepsy group (x2

ð1Þ ¼ 66:26, p< 0.001). As expected, anti-convulsive medication was significanthigher in the epilepsy group (x2

ð1Þ ¼ 265:79, p< 0.001).There were no statistically significant differences in sources of referral. However, in regards to care pathways, rates of

hospital admission were significant different between the groups (x2ð1Þ ¼ 6:99, p = 0.008) with patients with epilepsy having

lower rates of hospital admissions than patients without epilepsy (Table 3).

2.1. Multivariate analysis

Table 4 presents the logistic regression model for epilepsy. The presence of schizophrenia spectrum, personality andanxiety disorders were all independently associated with lower risk of being in the epilepsy group. The only variable

Table 2

Prevalence of ICD-10 co-morbid disorders and medication type by epilepsy.

Epilepsy, n (%) No epilepsy, n (%)

ICD-10 diagnosis

Schizophrenia 11 (7.1) 121 (20.3)

Personality disorder 6 (3.8) 51 (8.6)

Anxiety 7 (4.5) 47 (7.9)

Depression 11 (7.1) 51 (8.6)

Adjustment reaction 6 (3.8) 39 (6.5)

Dementia 6 (3.8) 21 (3.5)

Autism 26 (16.7) 21 (20.3)

No disorder 51 (32.7) 349 (58.6)

Medication

Psychotropic 11 (7.1) 181 (30.4)

Sedatives 2 (1.3) 27 (4.5)

Anticonvulsants 78 (50.4) 13 (2.2)

PRN 4 (2.6) 48 (8.1)

Combination 47 (30.1) 40 (6.7)

None 14 (9.4) 287 (48.2)

Table 3

Sources of referral and care pathways by epilepsy.

Epilepsy, n (%) No epilepsy, n (%)

Care pathways

ID psychiatry 105 (67.3) 423 (71)

Impatient unit 8 (5.1) 75 (12.6)

Outpatient 5 (3.2) 45 (7.6)

Referrals

Primary care 69 (44.2) 288 (48.3)

Social services 21 (13.5) 93 (15.6)

Generic MH 66 (42.3) 215 (36.1)

Table 4

Multivariate model: significant predictors for epilepsy.

Epilepsy B Exp (B) 95% CI

Schizophrenia �1.18 (0.34) 0.31** 0.16–0.61

Personality disorder �0.95 (0.46) 0.39* 0.16–0.95

Anxiety disorder �0.89 (0.43) 0.41* 0.18–0.96

Depression �0.30 (0.36) 0.74 0.36–1.51

Adjustment reaction �0.80 (0.43) 0.45 0.18–1.12

Dementia �0.11 (0.48) 0.90 0.35–2.32

Level of ID 1.39 (0.24) 4.10*** 2.51–6.45

Constant �1.16 (0.15) 0.31

* p< 0.05.** p< 0.01.*** p< 0.001.

S. Arshad et al. / Research in Developmental Disabilities 32 (2011) 353–357 355

associated with higher risk in the epilepsy group was severity of ID, with adults with severe ID being almost 4 times morelikely to be in the epilepsy group.

3. Discussion

In the present sample, 156 (20.7%) patients with ID had epilepsy in agreement with previous surveys (Morgan, Baxter, &Kerr, 2003). Some studies have reported a slightly higher prevalence of 26% (McGrother et al., 2006), although differentstudies have employed a variety of data collection methods, which may account for small differences in prevalence estimates(Fitzgerald & Ring, 2009). Moreover, patients with epilepsy and ID were less likely to be living independently, perhaps due tothe lower level of ID in this group which is often the strongest predictor of residential placement for those living incommunity settings (Chaplin et al., 2010).

In line with previous evidence (Branford et al., 1998; Forsgren, Edvinsson, Blomquist, Heijbel, & Sidenvall, 1990;Steffenburg, Hagberg, & Kyllerman, 1995) the present study also found that the presence of epilepsy was significantlyassociated with severity of ID (patients with severe ID were about four times more likely to have epilepsy than those withmild or moderate ID). Pawar and Akuffo (2008) found similar results with a three-fold increase of risk. Previous studiesconducted in this area have consistently reported high prevalence with increase in severity (McDermott et al., 2005). Thelifetime prevalence of epilepsy in those with mild to moderate (IQ 50–70) ID has been estimated to be about 15% whilst inthose with severe to profound (IQ> 50) ID a prevalence of 30% has been suggested (Fitzgerald & Ring, 2009).

Although there were no statistically significant differences in terms of age, the rates of epilepsy in the present sampleappeared to decline after the age of 45. A similar steady decline with progressing age has also been reported in previousstudies (Branford et al., 1998; McDermott et al., 2005). One possible explanation could be an increased risk of early mortalityassociated with epilepsy and therefore reduced prevalence in advanced age (Branford et al., 1998).

Until recently, five cohorts of adults with epilepsy and intellectual disabilities have been studied. Two comparedresidential patients with or without epilepsy with community controls (Espie, Pashley, & Bonham, 1989; Gillies, Espie, &Montgomery, 1989), one was comprised of both community and hospitalized participants (Deb & Hunter, 1991), another onecollected data from large residential developmental centre in USA (Matson et al., 1999) and the last and most recent onetakes a small residential sample from UK into account (Chung & Cassidy, 2001). A systematic review of these studies reportedno compelling evidence of epilepsy related to psychopathology (Espie, Watkins, & Curtices, 2003).

Our study finds no association between epilepsy and higher rates of psychopathology in adults with ID adding support toprevious evidence (Espie et al., 2003; Matthews et al., 2008). Most importantly, schizophrenia spectrum, personality andanxiety disorders were all independently associated with lower risk of being in the epilepsy group. This pattern of resultsappears consistent with previously reported trends (Pawar & Akuffo, 2008; Turkistani, 2004) which although statisticallynon-significant (sample sizes: N = 177 and N = 266 respectively) these were clearly significant effects in the present, largerstudy (N = 752).

As expected, anticonvulsant use was significantly higher in the epilepsy group. Patients with epilepsy also received lesspsychotropic medication and PRN (‘‘as required’’) medication, possibly due to the lower rates of psychopathology in thisgroup. It is conceivable that the tranquillizing effects of most anticonvulsant medication may result in little or no need forother psychotropic medication. Anticonvulsant medication is extensively used to treat non-epileptic disorders includinganxiety, schizophrenia and bipolar disorder (Johannessen, 2008).

The present results also showed that the presence of epilepsy does not affect referral process or services accessed,although there were significantly lower rates of inpatient hospital admission among those with epilepsy. They were also lesslikely to be referred to outpatient services. This pattern of results is consistent with the main finding that patients with IDand epilepsy had lower rates of co-morbid psychopathogy than those without epilepsy.

In conclusion, the present study demonstrated that rates of mental health problems such as schizophrenia spectrum,personality and anxiety disorders were significantly lower among patients with epilepsy who have been referred tospecialist mental health services. At the time of referral, most patients with epilepsy have been receiving anticonvulsantmedication for at least 2 years prior to the referral. It is therefore conceivable that mood-stabilizing and other psychotropiceffects of anticonvulsant medication may have moderated clinical symptoms. However, there is also the possibility ofdiagnostic overshadowing, with clinicians being perhaps less willing to give an additional mental health diagnosis topatients with epilepsy and ID. Such a possibility deserves further investigation as it has the potential to enhance ourunderstanding of the relationship between epilepsy and psychopathology in patients with ID and, therefore, increase theevidence base for clinical practice.

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